We had a few issues with the Cummins EGR systems on our first few that we got. The latest ones haven't had the issues of the others. So for now, we like the Cummins setup.

That being said for my rigs, the vollie's have had issues with the SRC engines. Mostly due to them not doing the regen when needed to. And no two volly departments are the same. One burns through DEF like crazy, the other doesn't. Engine temp and load on one is heavy, and uses less DEF. The other, drives light with less load on the engine, so it goes through DEF like crazy. It's hard to really explain, but there is a difference on engine load, miles driven, and engine temps, versus not working the engine as hard.